Vacuum arc devices with non-welding contacts

ABSTRACT

A triggerable vacuum gap discharge device having non-welding contacts is described as comprising a pair of electrode assemblies having interleaved vanes for establishing electrically parallel discharge paths therebetween and a pair of electrical contacts positioned outside the region of the discharge path, one of said contacts being movable into and out of engagement with the other contact. Triggering means are provided for injecting a concentration of charged conduction carriers into the electrically parallel gaps to cause electrical breakdown between the electrode assemblies whenever a voltage surge occurs in an electrical circuit in which the triggerable vacuum arc device is connected. If the voltage surge persists for more than a few cycles, the movable electrical contact moves into engagement with the other contact to prevent excessive erosion of the arc electrode assemblies.

United States Patent Lafferty Oct. 7, 1975 Primary Examiner-Robert S. Macon Attorney, Agent, or Firm-Marvin Snyder; Joseph T. Cohen; Jerome C. Squillaro [57] ABSTRACT A triggerable vacuum gap discharge device having non-welding contacts is described as comprising a pair of electrode assemblies having interleaved vanes for establishing electrically parallel discharge paths therebetween and a pair of electrical contacts positioned outside the region of the discharge path, one of said contacts being movable into and out of engagement with the other contact. Triggering means are provided for injecting a concentration of charged conduction carriers into the electrically parallel gaps to cause electrical breakdown between the electrode assemblies whenever a voltage surge occurs in an electrical circuit in which the triggerable vacuum arc device is connected. If the voltage surge persists for more than a few cycles, the movable electrical contact moves into engagement with the other contact to prevent excessive erosion of the arc electrode assemblies.

6 Claims, 3 Drawing Figures Ira US. Patent Oct. 7,1975 Sheet 1 of 2' 3,911,239

US. Patent Oct. 7,1975 Sheet 2 of2 3,911,239

VACUUM ARC DEVICES WITH NON-WELDING CONTACTS The present invention relates to vacuum gap devices and particularlythose of the triggered vacuum gap and vacuum switch type suitable for high current and high voltage circuit interruption.

Triggered vacuum switch interrupters generally comprise a pair of normally open contacts and triggering means for initiating an arc between the contacts upon the occurrence of a fault, such as a voltage surge on a line. Triggered vacuum switches of this type are normally placed in parallel with the device to be protected so that after an arc is initiated as a result of a fault, the contacts of the vacuum switch are closed to provide a metallic path for current flow and thereby prevent excessive erosion of the arcing contacts.

This mode of operation differs from that of the normal vacuum switch in which the contacts are normally closed and then opened to carry arcing current for /2 cycle or less and then remain open for a time while the contacts cool. In the case of the triggered vacuum switch described above, the contacts may be molten at the surface due to the large arcing currents when the contacts close. This condition could cause the contacts to weld together and not open again with normal forces exerted by the opening mechanism. I am aware of US. Pat. No. 3,489,873 Kurtz et a]. who disclose a triggered vacuum interrupter comprising spaced apart contacts which are movable into engagement with each other. This interrupter includes annular arc runners respectively surrounding the contacts and spaced apart from each other for providing a primary arcing gap therebetween. Means are provided for initiating an arc between the arc runners upon the occurrence of a fault but if the fault persists for more than a few cycles, the spaced apart movable contacts are driven into engagement thereby carrying the current previously carried by the arc.

It is therefore an object of this invention to provide an improved triggerable vacuum switch in which the surfaces of the vacuum switch are not exposed to prior arcing.

It is still a further object of this invention to provide a triggerable vacuum switch device in which contact between arc electrodes is made to cold surfaces to avoid welding.

Briefly, these and other objects and advantages of my invention are achieved in accord with one embodiment thereof by providing an hermetically sealed envelope with a hollow cylindrical member centrally located therein. Included in a first portion of the cylindrical member is a pair of arc electrode assemblies each having a plurality of substantially planar vanes projecting from the electrode assembly and interleaved alternately to define a plurality of electrically parallel gaps between the assemblies. Included in a second portion of the cylindrical member is a pair of electrical contacts, one stationary and the other movable into and out of engagement with the stationary contact. Means are provided within the first portion of the cylindrical member for injecting a concentration of charged conduction carriers into the parallel gaps to cause elec trical breakdown therebetween upon the occurrence of a fault. In the event that the fault should persist for more than a few cycles, the movable contact is driven into engagement with the fixed contact so that the are is extinguished between the arc electrode assemblies and the current path is through the engaged electrical contacts.

The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, together with further objects and advantages thereof may be more readily understood by reference to the appended drawings in which:

FIG. 1 is a vertical cross-sectional view of a triggered vacuum switch device constructed in accord with the present invention;

FIG. 2 is a horizontal cross-sectional view taken along the lines 22 of FIG. 1 illustrating the interleaved relationship of the arc-electrode assemblies; and

FIG. 3 is a perspective view of the central electrode structure of FIG. 1.

FIG. 1 illustrates an embodiment of a triggerable vacuum switch device 10 constructed in accord with one embodiment of the invention. The triggerable vacuum switch device comprises an evacuable envelope represented generally as 11 with a generally cylindrical member 12 including a first lower portion 13 and a second upper portion 14. The lower portion 13 of the cylindrical member 12 includes a pair of primary electrode assemblies including a central electrode assembly 15, illustrated in FIGS. 2 and 3 as comprising a plurality of outwardly depending radial vanes 16 which are fastened at their lowermost ends to a plate or disk 17. Each of the radial vanes 16 have a small thickness dimension as compared with its length and width dimensions and each vane is substantially perpendicular to each adjacent vane.

An outer electrode assembly 18 including the lower portion 13 of the cylindrical member 12 comprises a plurality of inwardly depending radial vanes physically and electrically connected together by the wall of said cylindrical member 12. The outer electrode assembly 18 surrounds the central electrode assembly 15. Electrode assemblies 15 and 18 are arranged so that the inwardly depending vanes 19 and the outwardly depending vanes 16 define a plurality of electrically parallel arcing gaps 20 therebetween. FIG. 2, a vertical cross section of FIG. 1, illustrates the interleaved relationship of the vanes 16 and 19 and the electrically parallel arcing gaps 20.

Affixed to the upper end of the central electrode assembly 15 and forming a part thereof is a disk-shaped electrical contact 22. The electrical contact 22 includes a high conductivity region 22a for making electrical contact to a movable electrical contact 23 (also including a high conductivity region 23a attached to a conductive support member 24 which is suitably mounted for vertical movement by a bellows assembly 25, for example. The bellows assembly 25 moves the electrical contact 23 into and out of engagement with the stationary contact 22 upon suitable actuation thereof.

The triggerable vacuum device illustrated in FIG. 1 also includes trigger means 26 adjacent the other end of the central electrode assembly 15 for initiating an arc across the gaps 20 between the radial vanes 16 and 19 of the electrode assemblies 15 and 18, respectively. The trigger means 26 comprises a trigger electrode 27 which passes through the lower portion of the evacuable envelope 11 to allow for connection of the trigger electrode to a suitable source of pulsed voltage, not shown. Upon application of such a pulsed voltage, the

trigger means 26 provides a pulse of gaseous ionelectron plasma or vaporized and ionized electrode material to cause breakdown between the electrode assemblies l5 and 18.

The triggerable vacuum device of FIG. 1 may be evacuated through a central tubulation 28 in the conductive support member 24 which terminates in a tubu lation 29, which after evacuation, is sealed to vacuum at the pinched-off portion 30. Means are also provided for making electrical connection to the conductive support member 24 and to the lower portion of the evacuable envelope at a contact 31. Between these two terminals, a source of alternating voltage 32 and a load represented by the impedance 33 may be connected in suitable circuit relationship.

Operationally, the triggerable vacuum switch device in accord with my invention may be utilized to protect against overvoltages on a power line system, such as the occurrence of an overvoltage on a series connected capacitor utilized for power factor correction. The device illustrated in FIG. 1, for example, would be connected directly across the power factor correction capacitor and means would be provided to sense an overvoltage across the capacitor and provide the aforementioned pulsed voltage to the trigger means 26 for supplying a pulse of gaseous ion-electron plasma or vaporized and ionized electrode material to cause breakdown in the electrically parallel arc gaps 20. The initiation of the plasma or are by the trigger means 26 produces an arc across the parallel arc gaps 20 which in turn establishes a low impedance path around the device to be protected, in this case, the power factor correction capacitor. In the event that the fault or overvoltage condition persists for more than afew cycles, the triggerable vacuum switch contacts 22 and 23 are closed to prevent excessive erosion of the radial vanes 16 and 19 caused by the arcing condition. The closure of the electrical contacts 22 and 23 extinguishes the arc in the parallel arcing gaps 20 and causes current to flow through the conductive path established by the conductive support member 24, engaged electrical contacts 22 and 23, central electrode assembly 15, and through the conductive regions of the device between the central electrode assembly and the contact 31.

As described above, the closure of contacts 22 and 23 is effected by a downwardly depending force applied to the upper portion of the conductive support member 24, such as by suitable solenoid drive means (not shown). Such closure of contacts 22 and 23 may be initiated immediately following the establishment of the are between the parallel arc gaps or after a suitable time delay, for example, a few cycles.

One of the significant advantages of my invention over prior art vacuum switches providing a similar function is the fact that the surfaces of the electrical contacts 22 and 23 are not subjected to the arcing that may occur in the parallel arc gaps 20. From the illustration of FIG. 1, it is apparent that the arcing is confined to the lower portion 13 of the cylindrical member 12, specifically to the parallel arcing regions 20. Hence, the electrical contacts 22 and 23 when engaged come together at cold surfaces that have not been exposed to arcing. Thus, there is no tendency for the contacts to weld or stick together after closure. This feature of my invention represents a substantial improvement over prior art vacuum switch devices in which the arc is initiated between the electrical contacts or in adjacent regions thereof that subject the contacts to the arcing conditions, thereby causing heating and melting of the contact surfaces. In accord with this invention, the electrical contacts are completely isolated from the arcing region and provide reliable non-welding contacting surfaces for conducting large fault currents.

Another advantage of my invention which results directly from the novel arrangement of the arcing electrodes and the switch contacts is the fact that the electrical contacting surfaces remain substantially smooth and unpitted after numerous fault protection cycles. This is particularly important in maintaining the low impedance path so that high continuous or fault currents can be carried repeatedly. I

In summary, I have disclosed an improved triggerable vacuum switch device useful in providing circuit protection for power line components which provides a high degree of reliability of operation and freedom from pitting and burning normally attendant to high current vacuum switch devices. The advantages flowing from my invention result primarily from the confinement of the arcing region to one portion of the device while providing closable electrical contacts in another portion of the device thereby insuring nonwelding of the contacts at time of closure.

While the invention has been set forth herein with respect to a specific embodiment thereof, numerous modifications and changes may readily be made by those skilled in the art. Accordingly, it is intended that the appended claims cover all such modifications and changes as fall Within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A triggerable vacuum gap discharge device comprising: an hermetically sealed envelope;

a hollow cylindrical member within said envelope;

a first arc-electrode assembly centrally located within said cylindrical member and including a plurality of thin, substantially planar vanes projecting outwardly therefrom;

a second arc-electrode assembly surrounding said first assembly and including a plurality of thin, substantially planar vanes projecting inwardly and supported by said cylindrical member, the vanes of said first and second electrode assemblies being interleaved alternately between one another to define a plurality of electrically-parallel gaps between said assemblies to cause electrical breakdown and arcing between said electrode assemblies to occur simultaneously at a multiplicity of points;

a stationary electrical contact connected to one end of said first arc electrode assembly;

movable electrical contact, movable into and out of engagement with said stationary contact;

means for injecting a concentration of charged conduction carriers into the electrically parallel gaps to cause electrical breakdown and arcing between said electrode assemblies; and

means for connecting said electrode assemblies and said electrical contacts in an electrical circuit.

2. The triggerable vacuum gap discharge device of claim 1 wherein said electrical contacts are located outside the region of said electrically parallel gaps.

3. The triggerable vacuum gap discharge device of claim 2 further comprising means for moving said movmeans adjacent the other end of said first electrode assembly.

6. The triggerable vacuum gap discharge device of claim 1 wherein said electrode assemblies are located in one portion of said cylindrical member and said electrical contacts are located in another portion of said cylindrical member so that said electrical contacts are outside the arcing region between the electrically parallel gaps. 

1. A triggerable vacuum gap discharge device comprising: an hermetically sealed envelope; a hollow cylindrical member within said envelope; a first arc-electrode assembly centrally located within said cylindrical member and including a plurality of thin, substantially planar vanes projecting outwardly therefrom; a second arc-electrode assembly surrounding said first assembly and including a plurality of thin, substantially planar vanes projecting inwardly and supported by said cylindrical member, the vanes of said first and second electrode assemblies being interleaved alternately between one another to define a plurality of electrically-parallel gaps between said assemblies to cause electrical breakdown and arcing between said electrode assemblies to occur simultaneously at a multiplicity of points; a stationary electrical contact connected to one end of said first arc electrode assembly; a movable electrical contact, movable into and out of engagement with said stationary contact; means for injecting a concentration of charged conduction carriers into the electrically parallel gaps to cause electrical breakdown and arcing between said electrode assemblies; and means for connecting said electrode assemblies and said electrical contacts in an electrical circuit.
 2. The triggerable vacuum gap discharge device of claim 1 wherein said electrical contacts are located outside the region of said electrically parallel gaps.
 3. The triggerable vacuum gap discharge device of claim 2 further comprising means for moving said movable electrical contact into and out of engagement with said stationary contact.
 4. The triggerable vacuum gap discharge device of claim 3 wherein said charged conduction carriers include gaseous ion-electron plasma and wherein the injection of said plasma into said electrically parallel gaps establishes a low impedance path for the conduction of electrical currents.
 5. The trigerable vacuum gap discharge device of claim 1 wherein said means for injecting a concentration of charged conduction carrier includes a trigger means adjacent the other end of said first electrode assembly.
 6. The trigerable vacuum gap discharge device of claim 1 wherein said electrode assemblies are located in one portion of said cylindrical member and said electrical contacts are located in another portion of said cylindrical member so that said electrical contacts are outside the arcing region between the electrically parallel gaps. 